The invention relates to n injector, in particular for common rail Diesel injection s stems of motor vehicles, having a multilayer piezoelectric actuator which has a multilayer actuator body, prestressed on a face end by a prestressing means and seated inside a longitudinal bore of an injector housing.
From International Patent Disclosure WO 94/19598 (Siemens AG), an injector of this kind with a multilayer piezoelectric actuator is known. The accompanying FIG. 1 shows the portion of the known injector located round the actuator body. In the known injector, the means that prestress the actuator body 1 comprise a cup spring 4 toward the valve, which on one end rests on or engages an annular flange 3 located on the face end toward the valve of the actuator body 1 and on the other end rests or engages a radially inward- protruding shoulder 5 of the injector housing 2. In this case, the injector housing 2 itself forms the means for transmitting the prestressing force, exerted by the cup spring 4, to the other face end of the actuator body 1. The arrow V indicates the direction toward the valve. Because of the diameter of the cup spring 4 acting as a prestressing element, the outside diameter of the injector housing 2, at the point where the spring action is most critical, that is, where the injector housing passes through a cylinder head wall, is relatively large.
The situation is similar for the other known common rail injector, shown in accompanying FIG. 2. An actuator body 1 seated centrally inside an injector housing 2 is prestressed, in the known injector shown in FIG. 2, is prestressed on its face end by a prestressing bracket 6 with a right and left spring leg 6a, 6b, by means of a first force-centering pressure member 7 and a second forcexe2x80x94centering pressure member 8. Since the two legs 6a, 6b of the prestressing bracket 6 require space on the left and right of the injector body 1, in this case as well it is not possible to reduce the outer diameter of the injector housing 2 in the critical region.
The result is that the prestressing elements used in conventional common rail Diesel injection systems of the prior art undesirably increase the diameter of the injector in the region of the piezoelectric actuator.
In order to make a common rail Diesel injection system with a multilayer piezoelectric actuator in a short structural design, the diameter of the components in the region of the actuator body must be selected to be as small as possible.
It is thus an object of the invention to make an injector with a multilayer piezoelectric actuator that is better suited to common rail Diesel injection systems of motor vehicles and in which the outer diameter of the injector housing can be as small as possible.
An essential aspect of an injector according to the invention with a multilayer piezoelectric actuator is that the prestressing means have at least one cup spring, which in prestressing fashion engages the face end of the actuator body opposite an injector valve, as well as a force transmission member seated in the injector housing and axially movable therein, which member transmits the spring force of the cup spring or springs to the face and, toward the valve, of the actuator body.
Preferably, the actuator body has a circular- cylindrical cross-sectional form. In this case, at least in the region of the actuator body, the sleevelike injector housing has a circular-cylindrical inner and outer contour and surrounds the actuator body and the force transmission member, which forms a circular-cylindrical clamping sleeve, and the actuator body abuts a radial inner wall, toward the valve, of the clamping sleeve, and the cup spring or springs engage between the opposed inner wall on the face end of the clamping sleeve and the adjacent face end of the actuator body.
Thus the cup spring or strings that effect the prestressing are provided behind the actuator body, that is, on the side of the actuator body remote from the valve, thus making a slender design of the injector in the region of the actuator body possible. In other words, the thicker actuator head having the cup spring or cup springs is located in the noncritical region of the cylinder head of the internal combustion engine.
With this arrangement, relatively short common rail injectors with a multilayer piezoelectric actuator that are no longer than the conventional magnet valve injectors can be produced.
The above and further advantageous characteristics of the injector of the invention will become even clearer in the ensuing description of a preferred exemplary embodiment when this description is read in conjunction with the accompanying drawings.